Ductility work hardening

Forming of built up edges may occur when machining ductile, work hardening materials at low cutting speeds and sufficiently steady chip formation. 

Pure metals are very soft indeed, and have a high ductility. This is what, for centuries, has made them so attractive at first for jewellery and weapons, and then for other implements and structures they can be worked to the shape that you want them in furthermore, their ability to work-harden means that, after you have finished, the... 

Austenitic steels have a number of advantages over their ferritic cousins. They are tougher and more ductile. They can be formed more easily by stretching or deep drawing. Because diffusion is slower in f.c.c. iron than in b.c.c. iron, they have better creep properties. And they are non-magnetic, which makes them ideal for instruments like electron microscopes and mass spectrometers. But one drawback is that austenitic steels work harden very rapidly, which makes them rather difficult to machine. 

All the stainless steels can be machined in the softened states, but they may present some problems unless the correct techniques are adopted. This is especially so with the austenitic grades where the extreme ductility minimises chip breaking and the work hardening may cause difficulties unless modest cuts are made. The free-cutting grades (those with high sulphur contents or selenium additions) are much easier to machine, but it must be remembered that they have somewhat reduced corrosion resistance, ductility and weldability compared to their normal counterparts. Detailed machining instructions are readily available from steel suppliers. 

Niobium is always found in nature associated with tantalum and it closely resembles tantalum in its chemical and mechanical properties. It is a soft ductile metal which, like tantalum, work hardens more slowly than most metals. It will in fact absorb over 90% cold work before annealing becomes necessary, and it is easily formed at room temperature. In addition, welds of high quality can be produced in the metal. In appearance the metal is somewhat similar to stainless steel it has a density slightly higher than stainless steel and a thermal conductivity similar to 1% carbon steel. 

H. Palladium. Palladium (mp 1,SS2°C), is soft and ductile but work-hardens. At elevated temperatures, the diffusion of hydrogen through palladium is rapid, which forms the basis of a method for the purification of hydrogen. The best performance is obtained from a palladium-silver alloy containing about 18% silver because, unlike pure Pd, this alloy does not undergo a phase transition in the presence of hydrogen. Palladium is not as inert as platinum and is attacked by sulfuric and nitric acids. 

During the deformation of ductile polymers there is often an increase in stress with deformation this is known as work-hardening. If at some point the stress is removed, the material recovers along a path nearly parallel to the linear region the sample then shows a permanent plastic deformation. 

High work-hardening rate combines cold-worked high strength with good ductility., Good structural qualities. Structural applications, bins and containers... 

Austenitic stainless steels are the most corrosion-resistant of the three groups. These steels contain 16 to 26 percent chromium and 6 to 22 percent nickel. Carbon is kept low (0.08 percent maximum) to minimize carbide precipitation. These alloys can be work-hardened, but heat treatment will not cause hardening. Tensile strength in the annealed condition is about 585 MPa (85,000 Ibf/in ), but workhardening can increase this to 2,000 MPa (300,000 Ibf/in ). Austenitic stainless steels are tough and ductile. 

The defects we have discussed in this chapter are largely microscopic and cannot be observed from the macroscopic structure of the materials. However, there are various sorts of macroscopic defect which can be examined using electron microscopy, and which explain certain physical characteristics. For example, metals are generally malleable and ductile but their ordered solid state structure implies that they should be rigid. Sometimes heating metals makes them more brittle in a process known as work hardening . These characteristics indicate that the structures of the metals are not perfect. The malleability of metals is an indication that the structure contains defects which occur in lines and planes, allowing the atoms to slip over each other. As the temperature rises or the metal is worked (as by a blacksmith), the metal becomes harder as the defects are removed. 

Aluminium is very malleable and ductile and easily formed into containers. During the process it is subject to work hardening which can be used to advantage in producing rigid containers. Alternatively the formed containers can be annealed to restore the softness and flexibility, e.g. in producing collapsible aluminium tubes. 

The LI 2 phase ZrjAl, which forms peri-tectically from ZrjAl and Zr, was studied extensively for use as the cladding material for water-cooled, nuclear power reactors since it has a low cross section for the absorption of thermal neutrons (Schulson, 1984 Liu et al., 1990 Parameswaran et al., 1990). In particular, the mechanical behavior was the subject of detailed studies (Schulson, 1984) according to which the strength is high with an anomalous temperature dependence for the flow stress. The work hardening rate exceeds that for any disordered or ordered f.c.c. alloy. ZrjAl, with polished surfaces, has a ductil-... 

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